Even though the frozen out species are conserved in the early universe but there can be some instances when dilution of these are possible due to the influx of entropy into the plasma. If the universe was dominated by primordial black holes of sufficient masses such that they evaporate in the matter dominated state, the influx of entropy can sufficiently reduce the existing baryon asymmetry and dark matter density, see [1]}, [2]}. QCD phase transition at \(T \sim 150-200~GeV\)  can also lead to this dilution as well, [3]}.
